In the related art, there is known a lens module that captures an image used for relatively low-profile web cameras for PCs and mobile terminals and that has three plastic lens arranged therein.
For example, the imaging lens disclosed in JP-A-2003-322792 has a short total length of the lens system including three lenses. Further, a lens having a shape whose both surfaces are aspheric is arranged closest to an image so as to reduce the incident angle of a main ray with respect to the entire imaging plane thus allowing application f an imaging element. While a single imaging lens has been used in related art in this field, the technology disclosed in JP-A-2003-322792 has made it possible to meet such needs as higher resolution of and magnification of an imaging element.
In case all of the three lenses are plastic lenses, there are variations in the focus position depending on the change in use temperature. This may be solved by introduction of the auto focus function although it is difficult to employ the auto focus function in low-profile devices such as mobile terminals. This is because of an enhanced space for a lens module, a decrease in the structural strength, a decreased mobility as a camera and increased manufacturing costs. Variations in the focus position caused by a change in temperature are solved by using three glass lenses although this approach is not favorable because of increased costs.